The use of liquid flow control valves, particularly of the rotatable type, such as the ball type, is well known to the art. Such valves are used at various points in a variety of chemical and process industries as well as in other fields, such as fire control, for the purpose of controlling and adjusting the amount or volume of liquid flowing through or being discharged from a flow line. In the discussion which follows, particular reference will be made to the ball type of flow control valve, but it will be understood that some aspects of the invention are applicable to any form of rotary valve member in which modulation of the flow control subjects the valve member to flow pressures which tend to change the position of the valve member unless some means is provided to prevent this from happening. Although the discussion will be directed primarily to manually controlled valves, as these are the most commonly used, it will be understood that the principles of the invention could apply equally to power-controlled or remote-controlled valves where the problems encountered may be similar to those encountered in manual operation.
The prior art structure of valves can broadly be classified into two categories; the flanged body type and the threaded body type and, in some instances, a combination of both. In those valves using a threaded body, the valve body is threadedly secured in the flow line so as to become a unitary part of the line. In the event that maintenance, repair or replacement of the valve becomes necessary, it is necessary to disassemble a portion of the flow line to disconnect and remove the valve. Where a flanged valve body is used, the problem of removing or disconnecting the valve body is less laborious and time-consuming than in the case of the threaded valve body, as it merely requires the removal of the flange bolts which serve to connect the flanged valve body to suitable flange members forming part of the flow line. However, in a flanged valve body, in contrast to the threaded valve body, a serious seal problem exists between the faces of the abutting flanges. This is commonly resolved by using some form of gasket material to prevent leakage and effect a seal. However, such seals are subject to rapid deterioration and require considerable replacements and preventative maintenance in order to avoid leaks, particularly under high pressure. Thus, though the threaded type of valve body does not have any significant leakage problem, it is difficult and time-consuming to remove such a threaded valve body for purposes of maintenance, repair or replacement, which necessarily involves expensive downtime for the flow line. On the other hand, the conveniently removable flange type of valve body involves less down-time for removal, but requires more frequent maintenance because of the above-described leakage problem.
Although rotary valve members tend to have lower friction losses and more effective flow control and modulation than other types of valve structures, there is a problem, particularly in high pressure flow systems for the valve member to shift or rotate in response to the pressure force exerted upon it by the fluid flow so that a predetermined flow setting, without some form of locking means, cannot be maintained using simple and uncomplicated valve adjusting arrangements.